Determination of the Young's angle using static friction in capillary bridges
Recently contact angle hysteresis in two-dimensional droplets lying on a solid surface has been studied extensively in terms of static friction due to pinning forces at contact points. Here we propose a method to determine the coefficient of static friction using two-dimensional horizontal capillary bridges. This method requires only the measurement of capillary force and separation of plates, dispensing with the need for direct measurement of critical contact angles which is notoriously difficult. Based on this determination of friction coefficient, it is possible to determine the Young's angle from its relation to critical contact angles (advancing or receding). The Young's angle determined with our method is different either from the value estimated by Adam and Jessop a hundred years ago or the value argued by Drelich recently, though it is much closer to Adam and Jessop's numerically. The relation between energy and capillary force shows a capillary bridge behaves like a spring. Solving the Young-Laplace's equation, we can also locate the precise positions of neck or bulge and identify the exact moment when a pinch-off occurs.